Coatings on fiber reinforced composites

ABSTRACT

The invention is a coating and a method for applying coatings to fiber reinforced composite materials. A first polymeric layer, free of fibers and particulate, coats a fiber reinforced polymer substrate. The first layer joins the fiber reinforced polymer substrate to a second polymeric layer. The second polymeric layer contains a polymeric matrix and a particulate within the polymeric matrix. Finally, at least one thermally sprayed material coats the second polymeric layer to form an adherent multi-layer coating attached to the fiber reinforced.

RELATED APPLICATION

This application claims the benefit of U.S. patent application Ser. No.09/507,769, filed Feb. 18, 2000, the entire teachings of which areincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to thermal spray coatings for fiber reinforcedpolymeric composites. This invention also relates to a process forproducing the coatings and to articles of manufacture having fiberreinforced polymeric composite components with the coatings.

BACKGROUND OF THE INVENTION

Fiber reinforced composite materials with polymeric matrices (FRP)including carbon fiber reinforced polymers (CFRP) can be designed andconstructed that have outstanding mechanical and physical propertiessuch as low density, high tensile and torsional strength, and highmodulus of elasticity or stiffness. A variety of high strength fibermaterials can be used including carbon fibers, glass fibers, siliconcarbide fibers, and fibers of many other oxides, carbides, and othermaterials. Similarly, a wide variety of polymeric materials can be usedincluding thermosetting resins such as phenolic resins, epoxies, andmany others. The fibers may be very long and positioned in specificpatterns or relatively short and randomly dispersed. When long fibersare positioned in specific patterns, they can be aligned in a singledirection or positioned in patterns designed to give two or threedimensional strength to the FRP. Thus the mechanical properties of theFRP structure can be tailored to the specific requirements of acomponent.

Unfortunately, the surfaces of a FRP have low resistance to wearincluding adhesive, abrasive, and erosive wear. They may also besusceptible to oxidation or other forms of corrosion, need protectionfrom heat, not have the required optical or electrical characteristics,etc. As a result, their utilization has been limited in manyapplications or has required the use of metallic or ceramic inserts orsleeves in areas of contact or exposure to wear, heat, etc. For example,a bulky and expensive wear resistant sleeve must be bonded to a FRPshaft in bearing areas to prevent adhesive or abrasive wear and FRPaircraft wing or tail components must have a metallic shield bonded onleading edges to prevent erosion. If the large rolls used in papermanufacturing and printing industries could be made of FRP they would bemuch lighter and stiffer thus much easier and safer to handle, requireless energy and time to accelerate and decelerate (due to lowerinertia), and produce better products due to rigidity. Their surface,however, would not have adequate wear resistance and could not beengraved as is required for some printing applications.

A solution to many of the problems associated with the utilization ofFRP would be an adherent coating with the required wear resistance orother properties. A wide variety of metallic, ceramic, cermet, and somepolymeric coatings can be produced using thermal spray deposition. Manyof these materials would be useful in providing wear resistance andother properties for FRP components if they could be successfullydeposited on them.

The family of thermal spray processes includes Super D-Gun™ deposition,detonation gun deposition, high velocity oxy-fuel deposition and itsvariants such as high velocity air-fuel, plasma spray, flame spray, andelectric wire arc spray. In most thermal coating processes, a metallic,ceramic, cermet, or some polymeric material in powder, wire, or rod formis heated to near or somewhat above its melting point and droplets ofthe material accelerated in a gas stream. The droplets are directedagainst the surface of the substrate (part or component) to be coatedwhere they adhere and flow into thin lamellar particles called splats.The coating is built up of multiple splats overlapping and interlocking.These processes and the coatings they produce have been described indetail in the following: “Advanced Thermal Spray Deposition Techniques”,R. C. Tucker, Jr., in Handbook of Deposition Technologies for Films andCoatings, R. F. Bunshah, ed., Second Edition, Noyes Publications, ParkRidge, N.J., 1994, pp. 591 to 642; “Thermal Spray Coatings”, R. C.Tucker, Jr. in Handbook of Thin Films Process Technology, Institute ofPhysics Publishing, Ltd., London, 1995; and “Thermal Spray Coatings”, R.C. Tucker, Jr., in Surface Engineering, ASM Handbook, Vol. 5, ASMInternational, Materials Park, Ohio, 1994, pp. 497-509.

In virtually all thermal spray processes, two of the most importantparameters controlling the structure and properties of the coating arethe temperature and the velocity of the individual particles as theyimpact on the surface to be coated. Of these, the temperature of theparticles is of greatest import relative to coating FRPs. Thetemperature the particles achieve during the deposition process is afunction of a number of parameters including the temperature andenthalpy (heat content) of the process gases, the specific mechanisms ofheat transfer to the particles, the composition and thermal propertiesof the particles, the size and shape distributions of the particles, themass flow rate of the particles relative to the gas flow rate, and thetime of transit of the particles. The velocity the particles achieve isa function of a number of parameters as well, and some of these are thesame as those that affect the particle temperature including thecomposition, velocity and flow rate of the gases, the size and shapedistributions of the particles, the mass injection rate and density ofthe particles.

In a typical detonation gun deposition process, a mixture of oxygen andacetylene along with a pulse of powder of the coating material isinjected into a barrel about 25 mm in diameter and over a meter long.The gas mixture is detonated, and the detonation wave moving down thebarrel heats the powder to near or somewhat above its melting point andaccelerates it to velocity of about 750 m/s. The powder's rapidly heatedinto molten, or nearly molten droplets of material that strike thesurface of the substrate to be coated and flow into strongly bondedsplats. After each detonation the barrel is purged with an inert gassuch as nitrogen, and the process repeated many times a second.Detonation gun coatings typically have a porosity of less than twovolume percent with very high cohesive strength as well as very highbond strength to the substrate. In the Super D-Gun™ coating process, thegas mixture includes other fuel gases in addition to acetylene. As aresult there is an increase in the volume of the detonation gas productswhich increases the pressure and hence greatly increases the gasvelocity. This, in turn, increases the coating material particlevelocity, which may exceed 1000 m/s. The increased particle velocityresults in an increase in coating bond strength, density, and anincrease in coating compressive residual stress. In both the detonationgun and Super D-Gun coating processes nitrogen or another inert gas canbe added to the detonation gas mixture to control the temperature of thedetonated gas mixture and hence the powder temperature. The totalprocess is complex, and a number of parameters can be used to controlboth the particle temperature and velocity, including the compositionand flow rates of the gases into the gun.

In high velocity oxy-fuel and related coating processes oxygen, air, oranother source of oxygen is used to burn a fuel such as hydrogen,propane, propylene, acetylene, or kerosene in a combustion chamber andthe gaseous combustion products allowed to expand through a nozzle. Thegas velocity may be supersonic. Powdered coating material is injectedinto the nozzle and heated to near or above its melting point andaccelerated to a relatively high velocity, up to about 600 m/s for somecoating systems. The temperature and velocity of the gas stream throughthe nozzle, and ultimately the powder particles, can be controlled byvarying the composition and flow rate of the gases or liquids into thegun. The molten particles impinge on the surface to be coated and flowinto fairly densely packed splats that are well bonded to the substrateand each other.

In the plasma spray coating process a gas is partially ionized by anelectric arc as it flows around a tungsten cathode and through arelatively short converging then diverging nozzle. The partially ionizedgas, or gas plasma, is usually based on argon, but may contain, forexample, hydrogen, nitrogen, or helium. The temperature of the plasma atits core may exceed 30,000 K and the velocity of the gas may besupersonic. Coating material, usually in the form of powder, is injectedinto the gas plasma and is heated to near or above its melting point andaccelerated to a velocity that may reach about 600 m/s. The rate of heattransfer to the coating material and the ultimate temperature of thecoating material are a function of the flow rate and composition of thegas plasma as well as the torch design and powder injection technique.The molten particles are projected against the surface to be coatedforming adherent splats.

In the flame spray coating process, oxygen and a fuel such as acetyleneare combusted in a torch. Powder, wire, or rod is injected into theflame where it is melted and accelerated. Particle velocities may reachabout 300 m/s. The maximum temperature of the gas and ultimately thecoating material is a function of the flow rate and composition of thegases used and the torch design. Again, the molten particles areprojected against the surface to be coated forming adherent splats.

Many attempts have been made to directly coat FRP surfaces with thermalspray coatings. Thermal spray coatings of metallic, cermet, or ceramiccompositions usually do not adhere at all or spall when only a smallamount of coating has been deposited. In most thermal spray coatingapplications, the surface to be coated must be roughened to provideadequate bonding. Roughening is usually done by grit blasting thesurface. Grit blasting or some other forms of roughening FRP surfacesleads to unacceptable erosion of the polymeric matrix and fraying of thefibers. The later, in particular, leads to a rough and porous thermalspray coating. This and other problems were found in attempting themethod of Hycner in U.S. Pat. No. 5,857,950 for example. Hycner teachesgrit blasting the surface of a CFRP fluid metering roll (an anilox rollused in printing) and then thermal spraying a layer of zinc, nickel-20chromium, or mixture of aluminum bronze plus 10 polyester at a negativerake angle of 11 M to 13 M degrees. A ceramic coating is then appliedover the first layer. The ceramic coating is subsequently finished andengraved. This process has been found to be unacceptable because of poorbond strength with some of the specified first layer coatings and otherproduction problems and because of substantial imperfections in thecoating. Many other attempts to use thermally sprayed metallicundercoats have also failed. Even attempts to deposit an undercoat of apolymeric material by thermal spraying were only marginally successfulin laboratory experiments and in production were difficult to reproducein a reliable manner.

An alternative method has been taught by Habenicht in EP 0 514 640 B1.Habenicht first creates on the surface of a CFRP a layer that consistsof a mixture of a synthetic resin that bonds to the CFRP and aparticulate material. After this layer is cured the surface is partiallyremoved to expose the particulate material. The particulate materialmust be capable of chemical bonding to the outer coating material thatis thermally sprayed on the first layer. The particulate materials andthe outer thermal spray coating material are selected from variety ofmetals and ceramics. While this method has met with limited success, themixture of synthetic resin and particulate material may not bond well tothe CFRP and tends to form balls of material on the surface, thus beingunsuitable for commercial production.

Several other techniques of preparing the surface of a CFRP surface forthermal spray coatings have been described by E. Lugscheider, R.Mathesius, G. Spur, and A. Kranz in the Proceedings of the 1993 NationalThermal Spray Conference, Anaheim, Calif., 7 to 11 Jun. 1993. One methodappears to be similar to that of Habenicht, but the most successfulmethod appeared to be one in which a three dimensional wire mat waslaminated into the polymeric composite. The surface was then gritblasted to expose the wire and a thermal spray coating applied. Thistechnique would be very expensive to use in industrial applications andwould tend to yield a very rough surface on the thermal spray coating.

Thus the current state of the art is such that there appears to be nomethod of successfully depositing thermal spray materials of a widevariety of compositions on FRP in a production worthy manner.

It is an object of the present invention to provide a coating for fiberreinforced composite polymeric materials and components that are wellbonded and have an exterior layer with high resistance to wear,corrosion or other unique properties not provided by the fiberreinforced composite materials.

It is further object of the present invention to provide a process forapplying well bonded thermal spray coatings to fiber reinforcedcomposite polymeric materials.

It is a particular object of the invention is to provide a thermal spraycoating and a method of applying thermal spray coating to carbon fiberreinforced composite materials and components.

SUMMARY OF THE INVENTION

The invention is a coating for fiber reinforced composite materials. Afirst polymeric layer, free of fibers and particulate, coats a fiberreinforced polymer substrate. The first layer joins the fiber reinforcedpolymer substrate to a second polymeric layer-two different composites.The second polymeric layer contains a polymeric matrix and a particulatewithin the polymeric matrix. Finally, at least one thermally sprayedmaterial coats the second polymeric layer to form an adherentmulti-layer coating attached to the fiber reinforced polymer substrate.

The process of the invention applies a coating on a fiber reinforcedcomposite material. It includes the steps of applying a first polymericlayer to a fiber reinforced polymer substrate. The first polymeric layeris free of fibers and particulate. Applying a second polymeric layercoats the first polymeric layer. The first polymeric layer acts as abonding agent to join the fiber reinforced polymer substrate to thesecond polymeric layer. The second polymeric layer contains a polymericmatrix and a particulate within the polymeric matrix. Thermal spraying amaterial coats the second polymeric layer, with the first and secondpolymeric layers protecting the fiber reinforced polymer substrateduring thermal spraying.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As noted above, it has been found that adequate thermal spray coatingson fiber reinforced composite materials can not be achieved using knownmethods. Surprisingly, it has been found that by applying a first layercomprising only polymeric materials and then a second layer comprising amixture of polymeric and particulate materials, that one or moreadditional layers of thermal spray materials can be applied. It isnecessary to judicially choose the polymeric materials in the twoinitial layers to achieve high bond strength between the first layer andthe FRP and between the first and second layer. With an appropriatechoice of materials, very well bonded coatings with no significantimperfections can be deposited.

The polymeric materials that may be used in either the polymeric firstlayer or as the polymeric material in the second layer comprising amixture of polymeric and particulate materials include epoxies andthermosetting resins. The preferred polymeric materials are epoxies andthe most preferred polymeric material is bisphenol F/epichlorohydrinepoxy resin (Shell Epon Resin 862) mean hydrogen equivalent weight ofcuring agent/epoxy equivalent weight of resin=20.7/170=0.1218 or 12.18weight percent of curing agent diethylenetriamine (Epi-Cure 3223), a twopart epoxy that cures at room temperature. The first polymeric layerremains free of fibers and particulate to ensure a strong bond to theFRP.

The surface of the FRP must be cleaned prior to the application of thefirst layer. Appropriate solvents may be used to remove any oils orother contaminants. It is preferred that the surface be roughened afterit has been cleaned, preferably to a roughness of not less than 3.048microns (120 microinches) Ra. Grit blasting can be used to accomplishthe surface roughening. Residual debris and other contaminants can beremoved by wiping with an appropriate solvent such as methanol oracetone.

A variety of methods may be used to apply the first layer of polymericmaterials. The choice of method is dependent, in part, on the geometryof the surface to be coated and the composition and physicalcharacteristics of the polymeric material. The methods include spreadingthe polymeric material on surface if it is sufficiently viscous,spraying atomized droplets of the materials using typical liquid spraydispensers or any other method of applying a liquid to a surface.Spreading a viscous material on the surface may be done manually or withan automated or semi-automated system. A doctor blade may be used tocontrol the thickness of the layer. The polymeric material may beapplied by spraying, if the viscosity is low enough or a diluent isadded to the polymeric material to reduce its viscosity sufficiently toallow spraying. The preferred method is to spread the polymeric materialon the surface as somewhat viscous material, most preferably using anautomated or semi-automated method. If the surface to be coated iscylindrical in shape, the cylinder can be rotated and the polymericmaterial applied to the surface by feeding it onto a blade held parallelto an element of the cylinder surface and at a distance suitable tocontrol the thickness of the layer. The polymeric material is thenallowed to flow off of the blade surface onto the cylinder surface as asmooth sheet of uniform thickness. The thickness is thus controlled andno mist or overspray is released into the atmosphere as is the case inspraying. Preferably only a thin layer of the polymeric material isapplied to the surface of the FRP, just sufficient to wet the surface.The preferred thickness of the layer comprising a polymeric layer is inthe range of about 0.002 to 0.127 mm, with the most preferred rangebeing about 0.005 to 0.076 mm.

The second layer of the coating system comprising a mixture of polymericand particulate materials is usually applied over the first layercomprising a polymeric material before the first layer is cured; i.e.,while the first layer is still tacky. Alternatively, the first layercomprising a polymeric material is cured after it is applied. Ifnecessary, and a thick enough layer is applied, the cured first layermay be machined by grinding or other methods to smooth and adjust thethickness of the layer.

The particulate material in the second layer may be at least onematerial selected from the group consisting of metallics, cermets, andceramics. Most advantageously, the particulate is at least one materialselected of the groups consisting of: Group I, aluminum, nickel, iron,chromium, and cobalt; Group II, aluminum-base, nickel-base, iron-base,chromium-base, and cobalt-base alloys; Group III, aluminum, chromium,zirconium and silicon oxides; Group IV, aluminum, chromium, zirconiumand silicon compounds; Group V, chromium, tungsten, boron, siliconcarbides; and Group VI, boron and chromium nitrides. The size of theparticulate material is dependent on the specific composition of theparticulate material, but may be from essentially zero to about 500 μm(less than approximately 50 mesh). The preferred size for greater than90% of the material for aluminum is −127/+78 μm screen size (−200/+325mesh), for nickel is −149/+78 μm screen size (−170/+325 mesh), and foriron −318/+78 μm screen size (−80/+325 mesh). For other particulatematerials, the preferred size is −318/+64 μm screen size (−80/+400mesh). The amount of particulate material in the second layer is afunction of the composition of the particulate material, the geometry ofthe component being coated, and the method of application as smallchanges in composition can change the viscosity of the mixturesignificantly. In weight percent, the preferred amount of particulatematerial is in the range of about 20 to 85, and the most preferredamount is in the range of about 60 to 80.

The second layer of the coating system comprising a mixture of apolymeric material and a particulate material may be applied by any ofthe methods described above for the first layer comprising a polymericmaterial. The method used for the first layer may be different than thatused for the first layer, however, depending on the physicalcharacteristics of the mixture. For example, the first layer may besprayed and the second spread. Nonetheless, the preferred method forapplying the second layer is by spreading manually or in an automated orsemi-automated manner. If the surface to be coated is cylindrical inshape, the most preferred method is by feeding the mixture onto a bladeheld parallel to an element of the cylinder and at a distance suitableto control the thickness of the layer. The mixture is then allowed toflow off of the blade onto the cylinder surface as a smooth sheet ofuniform thickness. The preferred thickness of the layer comprising amixture of polymeric and particulate materials is in the range of about0.05 to 3.2 mm, with the most preferred range being about 0.5 to 1.27mm.

The second layer comprising a mixture of polymeric and particulatematerials is cured after it is applied. If necessary, the cured secondlayer may be machined by grinding or other methods to smooth the surfaceand to adjust the thickness of the layer. The roughness of the surfaceof the second layer may then be optimized to increase the strength ofthe bond of the subsequently applied thermal spray coating to it. Thepreferred method of surface roughening is grit blasting. Preferably,grit blast parameters are chosen to obtain the maximum roughness withoutremoving more than about a 0.025 mm thick layer of material from thesurface.

One or more layers of thermal spray coatings are applied by any thermalspray method over the suitably prepared layer comprising a mixture ofpolymeric and particulate material. Although any thermal spray methodmay be used, the preferred method is plasma spray deposition. Metallic,ceramic, cermet, and some polymeric materials may be deposited bythermal spray. As noted above, the specific thermal spray coatingmaterial is selected based on the requirements of the serviceenvironment. Enhanced mechanical properties may be achieved by using twoor more layers of thermal spray coatings of different compositions. Forexample, the first or inner thermal spray layer may be a metal or metalalloy such as nickel or a nickel-chromium alloy and the second or outerlayer an oxide such as chromium oxide. Such a two layer thermal spraycoating system may have a higher bond strength and greater resistance toimpact damage than a single layer of chromium oxide. The thickness ofthe thermal spray coating layer or layers is dependent on therequirements of the service environment including the expected wear lifeand mechanical properties. The preferred thermal spray coating thicknessrange is about 0.05 to 0.5 mm. The preferred thickness range is about0.05 to 0.25 mm for the initial metallic thermal spray coating when twoor more thermal spray coating layers are used.

This invention is applicable to the coating of many articlesmanufactured using fiber reinforced composites to enhance the wear,corrosion, and other properties of their surfaces. Virtually anycomponent geometry that can be coated using thermal spray technology (aline-of-sight deposition process) can be coated using the methods ofthis invention. Some of the most readily coated component surfaces arethose that are either flat or cylindrical in shape. Cylinders areusually coated by rotating them about their axis and simultaneouslyapplying the coatings by moving the spreading or spraying applicationalong the length of the cylinder. Both the rate of rotation and the rateof traverse down the length of the cylinder are chosen to uniformlyapply the coatings at a prescribed rate of deposition in one or morepasses.

FRP cylinders of particular importance are rolls used in the printingand in the paper industry as noted in the background section herein. Inthe printing industry, anilox rolls are used to transport very preciselymeasured amounts of ink from a reservoir to the printing roll.Currently, the most advanced rolls of this type are made of metal with aplasma sprayed chromium oxide surface. The chromium oxide is firstground to a smooth surface and then engraved using a laser with verysmall holes. Ink is adsorbed on the surface as the roll rotates througha reservoir. The excess ink is scrapped from the surface by a doctorblade and then the remaining ink contained in the holes is transferredto the printing roll. The roll surface must be both resistant tocorrosion by the ink and resist wear by the doctor blade. An idealmaterial for this application is chromium oxide. For the reasons notedin the background section, it would be highly advantageous to changefrom a metallic roll body to a carbon fiber reinforced polymericcomposite roll body. After repeated unsuccessful trials using thevarious methods known in the art, it was found that the methods of thisinvention yielded a uniquely reproducible and production worthy coatingsystem for this application.

The preferred coating system for anilox rolls consists of a first layercomprising an epoxy-based polymeric coating about 0.005 to 0.076 mmthick, a second layer comprising a mixture of an epoxy-based polymericcoating and a particulate material about 0.5 to 1.27 mm thick, a thermalspray coating layer of a metal or metal alloy about 0.05 to 0.25 mmthick, and a thermal spray coating of chromium oxide about 0.01 to 0.5mm thick. The most preferred epoxy based polymeric material in both thefirst and second layer is bisphenol F/epichlorohydrin epoxy resin+12.18weight percent diethylenetriamine. The preferred particulate material inthe mixture of the second layer mixture is selected from the groupconsisting of metals, ceramics, and cermets. The most preferredparticulate material in the mixture of the second layer is selected fromthe group comprising aluminum, aluminum alloys, nickel, nickel alloys,or iron alloys. The preferred amount of particulate material in weightpercent in the mixture of polymeric and particulate materials in thesecond layer is about 20 to 85. The most preferred amount of particulatematerial in weight percent in the mixture of the second layer is about58 to 64 for aluminum and about 71 to 77 for nickel. The preferred metalof the first thermal spray layer is selected from the group consistingof nickel, chromium, iron, zinc, and their alloys. The most preferredmetal of the first thermal spray layer is selected from a groupconsisting of nickel and nickel alloys. The preferred method of applyingthe polymeric layer and the layer comprising a mixture of polymeric andparticulate materials is by spreading. The preferred thermal sprayprocess for both the metallic and chromium oxide layers is plasma spraydeposition.

FRP rolls for use in the paper industry may be coated in a mannersimilar to that used for anilox rolls as described above, but with analumina-based outer coating rather than chromia-based. For theseapplications, the alumina is not usually laser engraved.

The following examples are provided below to illustrate the invention,but are not intended to demonstrate the full scope of the invention orlimit its applicability in any way. Examples 1 to 6 representcomparative examples outside the scope of the invention.

EXAMPLE 1

Many attempts were made to coat several types of carbon fiber and glassfiber reinforced composite materials directly with plasma sprayedchromium oxide and with plasma sprayed nickel coatings. The surfaceswere roughened to varying degrees by grit blasting and the depositionparameters were varied, but without success. Virtually no deposition ofchromium oxide was achieved and the coverage achieved with nickel wasincomplete and the carbon fibers flared even more than after gritblasting. A few samples were coated with a first layer of nickel about0.25 mm thick followed by a second layer of chromium oxide. The bondstrength of some of these nickel/chromium oxide coatings to CFRP wasmeasured using a modified American Society for Testing and Materialstensile bond test designed for thermal spray coatings. The maximum bondstrength achieved was 1,100 psi (7.6 MPa) when the chromium oxide layerwas 0.175 mm thick, diminishing to near zero when the chromium oxidelayer was 0.300 mm thick. These values are unacceptable for service use.

EXAMPLE 2

An attempt was made to coat a carbon fiber reinforced composite with adiluted epoxy based material prior to attempting to deposit chromiumoxide or nickel by plasma spraying. Virtually no chromium oxide wasdeposited whether it was plasma sprayed while the epoxy-based layer wasstill tacky or completely cured.

EXAMPLE 3

Carbon fiber reinforced composites samples were electroplated withnickel greater than 0.5 mm thick and then ground to about 0.175 to 0.200mm thick. Nickel coatings about 0.125 mm thick were also produced. Bothwere successfully over-coated with plasma sprayed chromium oxide. Anelectroplated nickel coating about 0.125 mm thick was tested; but itspalled when a plasma sprayed chromium oxide was applied over it. Whilethis approach to coating CFRP appeared to be somewhat successful, itsreproducibility is questioned. Furthermore, this process requires anelectroplating facility and it would be very expensive to apply to largecomponents.

EXAMPLE 4

Carbon fiber reinforced composite samples were coated with resin-bondedhollow microspheres which were then ground to open the hollow spheres toprovide cavities for bonding a second coating. Some of the samples werethen over-coated with plasma sprayed stainless steel. An attempt wasthen made to coat these samples with plasma sprayed chromium oxide. Theunderlying resin bonded microsphere coating spalled in all cases.

EXAMPLE 5

Carbon fiber reinforced composite samples were obtained that had a whitegel (resin) overcoat. These samples could be coated with a plasmasprayed chromium oxide, but it was found that the chromium oxide coatinghad many pinholes and small areas with no chromium oxide coating. Inaddition, the white gel process was difficult to use in productionbecause of the excessive amount of diluent, methyl ethyl ketone thatevolved during spraying resulting in: 1) creating a potential health andfire hazard; 2) difficulty in obtaining a uniform coating; and 3)difficulty in maintaining its uniformity while the coating was cured.

EXAMPLE 6

A series of experimental CFRP samples and prototype rolls were coatedwith the following procedure. Process parameters were optimized for eachstep in the procedure.

The CFRP was cleaned and then roughened by grit blasting with 60 meshaluminum oxide grit at 20 psi and a 152 mm standoff to a surfaceroughness of greater than 0.003048 mm (120 microinches) Ra. The surfacewas then wiped with methanol or acetone.

A mixture of an epoxy and either aluminum or nickel was produced. Theepoxy was a mixture of bisphenol F/epichlorohydrin (Shell Epon862)+12.18 weight percent diethylenetriamine (Shell Epi-Cure 3223). Inthe case of aluminum, the mixture was 60 to 62 weight percent aluminum.In the case of nickel, the mixture was 73 to 75 weight percent nickel.The metal powders were nominally less than 44 microns in size. Theviscosity changes significantly within the composition ranges given, andthe specific ratio used was chosen for ease of application on a specificsample or component. Great care was taken to avoid introducing air intothe mixture while blending the epoxy with the metal powder. A number ofattempts were made to spread the mixture on the sample or componentusing techniques described above. None of these attempts weresuccessful.

EXAMPLE 7

It was surprisingly found that the addition of a thin layer of polymericmaterial on the FRP surface served to enhance the bond strength and thereliability of the coatings. The following illustrates the coatingmaterials and processes used to successfully coat both laboratorysamples and production prototype anilox rolls made of carbon fiberreinforced composite materials.

The CFRP was cleaned and then roughened by grit blasting with 60 mesh(−423 μm screen size) aluminum oxide grit at 20 psi (138 kPa) and a 152mm standoff to a surface roughness of greater than 0.003048 mm (120microinches) Ra. The surface was then wiped with methanol or acetone.

A thin layer of epoxy was then applied to a thickness of 0.005 to 0.025mm. The epoxy was a mixture of bisphenol F/epichlorohydrin (Shell Epon862)+12.18 weight percent diethylenetriamine (Shell Epi-Cure 3223). Theepoxy was applied smoothly to the sample or roll surface shortly (lessthan 20 min.) before the mixture of epoxy plus aluminum was applied.

A mixture of the same epoxy as in (b) above and either aluminum ornickel was produced. In the case of aluminum, the mixture was 60 to 62weight percent aluminum. In the case of nickel, the mixture was 73 to 75weight percent nickel. The metal powders were nominally less than 44microns in size. The viscosity changes significantly within thecomposition ranges given, and the specific ratio used was chosen forease of application on a specific sample or component. Great care wastaken to avoid introducing air into the mixture while blending the epoxywith the metal powder. The mixture was spread on the sample or componentusing a technique described above to a thickness of about 0.500 mm.

The epoxy and epoxy/metal mixture was allowed to cure for at least threehours and then single point machined to a thickness of about 0.300 mm.

After at least 36 hours from the time the epoxy/metal mixture wasapplied, the surface can be roughened by grit blasting using 60 mesh(423 μm screen size) aluminum oxide grit at 20 psi (138 kPa) with a 150mm standoff to a surface roughness of about 0.00508 to 0.00635 mm (200to 250 microinches) Ra.

Optionally, a plasma deposited nickel coating was then applied to athickness of about 0.125 mm.

A plasma deposited chromium oxide coating was applied to a thickness ofabout 0.300.

For a prototype anilox roll, the chromium oxide coating was ground to asmooth surface and then laser engraved.

All of the samples prepared by this procedure were very acceptable. Nosignificant surface imperfections were observed. The bond strengths ofthe coating systems with and without the optional plasma sprayed layerwere measured using a modified recommended procedure of the AmericanSociety for Testing and Materials. A tensile bond strength of 3010 psi(20.8 MPa) was measured with the nickel layer and 3200 psi (22.1 MPa)without the nickel layer. Thus the bond strength for either was morethan adequate for the intended service as an anilox roll. Themulti-layer structure readily achieves the 10 MPa tensile strengthrequired for most commercial applications.

The process readily coats cylindrical rolls constructed with fiberreinforced polymer substrates such as CRFPs. First applying the twopolymeric layers to a cylindrical roll's outside cylindrical surface andthen thermally spraying this surface creates the multi-layer coatingthat effectively covers and protects the roll's working surface. This isparticularly effective for articles of manufacture such as fluidmetering rolls, rolls used in the production of paper and rolls used infilm processing.

The multi-layered structure provides an effective coating for fiberreinforced composite polymeric materials and components. These coatingsare well bonded and have an exterior layer with high resistance to wear,corrosion or other unique properties not provided by the fiberreinforced composite materials per se. In addition, it provides animproved process for applying well bonded thermal spray coatings tofiber reinforced composite polymeric materials and in particular tocarbon fiber reinforced composite materials and components.

Many possible embodiments may be made of this invention withoutdeparting from the scope thereof, it is understood therefore that allmatter set forth herein is to be interpreted as illustrative and not ina limiting sense.

1. A process of applying a coating on a fiber reinforced compositematerial comprising the steps of: a) applying a first polymeric layer toa fiber reinforced polymer substrate, the first polymeric layer beingfree of fibers and particulate; b) applying a second polymeric layercoating to the first polymeric layer to join the fiber reinforcedpolymer substrate to the second polymeric layer using the firstpolymeric layer as a bonding agent, the second polymeric layercomprising a polymeric matrix and a particulate within the polymericmatrix; and c) thermal spraying a material to coat the second polymericlayer with the first and second polymeric layers protecting the fiberreinforced polymer substrate.
 2. The process of claim 1 including theadditional steps of roughening the surface of the fiber reinforcedcomposite substrate before applying the first polymeric layer; androughening the surface of the second polymeric layer before thermalspraying the material on to the second polymeric layer.
 3. The processof claim 1 wherein the fiber reinforced polymer substrate is acylindrical roll having an outside diameter surface and the applying thefirst polymeric layer consists of coating the outside cylindricalsurface of the cylindrical roll.
 4. The process of claim 1 wherein thefirst and second polymeric layers are a bisphenolF/epichlorohydrin+diethylenetriamine, the particulate material in thesecond polymeric layer is aluminum or nickel, and the thermally sprayedmaterial is a single layer of chromium oxide or a multi-layer consistingof an inner nickel layer and an outer chromium oxide layer.